ITASE scientists reconstruct recent Antarctic climate in unprecedented detail
Posted March 28, 2008
One might be forgiven for assuming Antarctica is one uniform block of ice given a superficial view from an airplane. The white horizon seems to stretch on forever, occasionally interrupted by mountain peaks, appearing like rough speed bumps on its smooth surface.
But scientists interested in the physical processes that drive the continent’s dynamic ice flow see a different picture. Zooming in with the use of satellites and radars, they find dramatic changes in ice mass at the edges, particularly in West Antarctica. On the ground, they can take ice cores that will tell them about past climate by analyzing various properties like density and chemical composition.
Researchers involved in the United States component of the International Trans-Antarctic Scientific Expedition (ITASE) make use of all these tools and more as they attempt to reconstruct the continent’s climatic history over the last 200 to 1,000-plus years.
Their goal is to create a season-by-season record of environmental change for Antarctica, taking it from the least-understood continent to the most-understood one on the planet for the last several hundred years. And they’re rapidly approaching that goal, according to Paul Mayewski, the principal investigator for ITASE.
“Antarctica is so well suited [for understanding climate] because literally anywhere you go you can recover an ice core,” he explained. “We have … buried archives lying around anywhere we [can] extract them and analyze them.”
U.S. ITASE scientists have made six traverses across parts of the continent since 1999 — four in West Antarctica and two in East Antarctica — collecting more than 40 ice cores and many gigabytes of radar data. Twenty-one nations now comprise ITASE, many of them conducting their own overland journeys as they cooperatively build this unprecedented database.
“ITASE is an important international activity, which brings together scientists from most of the [Scientific Committee on Antarctic Research] nations, and it has become a central focus of much of the recent shallow ice coring activity around the continent,” noted Julie Palais, glaciology program manager at the National Science Foundation’s Office of Polar Programs.
“In addition, ITASE traverses are an important component of the on-going International Polar Year activities being supported by the U.S. and other countries,” she added.
Mayewski and his team started their most recent traverse expedition during the 2006-07 austral season after a three-year hiatus. The self-supported journey by farm tractor and sled began at Taylor Dome, an ice ridge that rises about 2,400 meters above sea level.
Equipment snafus limited the team to about 460 kilometers that season, but it got back on track this past summer, arriving at the South Pole on Christmas Eve 2007. “Basically, this year we were able to get back to our old mode of operation,” said Brian Welch, a researcher from St. Olaf College in Minnesota, who operated the team’s deep radar system. The deep radar can peer down 3,500 meters to the bedrock beneath the ice sheet.
“It was nice to finish this series of six seasons off, and this second of two seasons, with a nice, straightforward program,” added Mayewski, director of the Climate Change Institute at the University of Maine and founder of the 21-nation ITASE effort. “Things went very well this year, the way they have characteristically for most of our projects.”
The scientists have much to analyze, but they can make some general statements about their findings, the foremost that the interior surface regions of Antarctica haven’t changed much in the centuries they targeted.
“Temperature, precipitation and circulation systems that get in there are probably still within the range of variability within the last few hundred years,” Mayewski said. “As you go out to the coastal areas, however, or if you go into the ocean or go into the winter atmosphere above Antarctica, they’re all indicating warming.”
Mayewski explained the results for the interior regions aren’t too surprising considering the extreme inland temperatures, which can plunge below minus 70 degrees Celsius (minus 100 degrees Fahrenheit) in the winter. A couple degrees of difference, he said, aren’t going to alter significantly the deep-freeze climate in these regions.
“Snow accumulation in the interior isn’t changing yet, even though there’s a bit of warming,” he added. “[That’s] important because that means that sea level contribution of melting Antarctic ice is not necessarily being offset by snow accumulation due to slightly warmer air masses coming into Antarctica.”
It’s what the polar scientists refer to as ice mass balance. The question they want to understand: Is the amount of ice discharged into the ocean by glaciers and the calving of ice shelves being offset by precipitation over the continent? The answer coming from ITASE and other researchers is “no, so far.”
Welch said that, in fact, accumulation rates are regionally variable. Some areas are actually moving into negative territory due to wind scour. “We see a lot of erosion surfaces in East Antarctica,” he explained.
And that thick ice sheet may not be as invulnerable as many believe, Welch said, should the changes chipping away at the continent’s edges propagate inland.
“We’re finding that water is much more prevalent beneath the ice sheet, particularly in East Antarctica, than we ever thought it was before,” he explained. “Water allows the ice to slide and the glaciers to move much faster, and subsequently respond much quicker [to warming].
“What we’re finding is that there seems to be water everywhere we look,” he added.
That information comes from the deep radar, which Welch explained, is sort of the radio equivalent of a fish finder. In the case of the radar, it picks up differences in the electrical conductivity of the ice rather than density. So it can pick out thin layers in the ice like sulfuric acid, likely from a volcanic eruption, or the presence of water.
“We have a very sensitive system that can detect very small changes,” he said. “It gives us more information with what’s happening to the ice sheet as a whole.”
The deep radar found several subglacial lakes along the route this year, two of which may be previously undiscovered, according to Welch. The role the lakes play in the hydrology of the continent is not well understood, but it appears many of them periodically drain and then refill with surrounding melt water. “What we believe is going on with most of these lakes is that they fill, drain, fill, drain on a somewhat regular basis,” he said.
Said Mayewski of the ITASE program, “Slowly but surely, little bits and pieces of the puzzle are starting to come together.”
To unravel that puzzle further, Mayewski said the ITASE program would shift its focus to the edges of the continent, where dramatic changes in ice flow and temperature are taking place. That means parking the heavy tractors for a while, because those areas slope sharply and boast innumerable crevasses.
“A lot of emphasis for the next few years will be the more coastal sites,” he said.
NSF-funded research in this story: Paul Mayewski, Climate Change Institute at the University of Maine; Brian Welch, St. Olaf College.
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